A magneto-optical disk has been researched and developed as an optical disk which is capable of rewriting, and part of magneto-optical disks has been already put to practical use as an outer memory for a computer.
A magneto-optical disk is characterized by that its recording capacity is larger than that of a floppy disk or a hard disk utilizing an in-plane magnetization film because a vertical magnetization film is used as a recording medium so that recording and reproducing are carried out by using a light.
As shown in FIG. 12, address information of a track where information is recorded and reproduced is recorded on a land 52 by a pit row 53 between grooves 51.51 formed in a magneto-optical disk so that the address information of the track corresponding to the land 52 which is scanned by an optical spot 55 can be obtained.
A track pitch is set as an about value which is same as diameter of the optical spot 55, and a diameter of the optical spot 55 is determined by a wavelength of a laser beam and a numerical aperture of an object lens for converging the laser beam as an optical spot 55. A wavelength of a laser beam is usually 780 to 830 nm, and a numerical aperture of the object lens is 0.45 to 0.6. Therefore, a diameter of the optical spot 55 becomes 1.2 to 1.4 .mu.m, and the track pitch is also set as 1.4 to 1.6 .mu.m. For this reason, a size of a recording domain 54 in which magnetization is upward or downward becomes about 0.8 .mu.m which is a smallest value.
In recent years, in such a magneto-optical disk, a system for forming a plurality of magnetic layers of a recording film so as to reproduce recording bit which is smaller than the optical spot 55 by a magnetic super-resolution is suggested in order to improve recording density (For example, see Japanese Unexamined Patent Publication 5-81717/1993 (Tokukaihei 5-81717) and Japanese Journal of Applied Magnetics 1991, vol. 15, No. 5, pp.838-845). According to these suggestions, since a recording bit with a size of 1/2 of the above one can be reproduced, a track pitch can be also reduced to substantially 1/2, namely, about 0.8 .mu.m.
In addition, as shown in FIG. 13, in a phase-changing-type optical disk in which a recording domain 58 is formed on a groove 56 and a land 57, a method for reducing crosstalk of a recording signal which is entrance of noise from adjoining tracks (for example, (1) CONFERENCE DIGEST 1992 No. 3, 18a-T-2, pp.948; 53rd SYMPOSIUM ON APPLIED PHYSICS and (2) Improvement of track density by land and groove recording on phase change optical disk; CONFERENCE DIGEST July, 1993 pp. 57-58; JOINT INTERNATIONAL SYMPOSIUM ON OPTICAL MEMORY AND OPTICAL DATA STORAGE).
However, with the above conventional arrangement, when a track pitch is 1/2, for example, a distance between pits 53 on the adjoining tracks becomes 1/2. For this reason, crosstalk which causes inclusion of an address signal of the pit row 53 on a next track becomes larger, so there arises a problem that accurate address information cannot be obtained.
In addition, when the pit row 53 which gives address information respectively is formed on the groove 56 and the land 57, there also arises a problem that a process for producing an optical disk becomes complex.